The present invention relates to a retractor locking mechanism for vehicle safety restraints and particularly to such a mechanism for a retractor fitted a with pretensioner.
Known retractors for vehicle safety restraints have two sensors. A so-called vehicle sensor detects rapid acceleration or deceleration of the vehicle, indicative of a crash situation, and operates a locking mechanism in response to such a condition to prevent further webbing withdrawal from the retractor. A webbing sensor traditionally uses an inertia disc rotating with the spool to detect rapid withdrawal of webbing, again indicative of a crash situation, and to lock the webbing spool against further rotation in response to such rapid withdrawal.
Recently pretensioning systems have been incorporated to improve safety restraints. These devices take up slack in the webbing to more securely locate the vehicle occupant in his seat in the event of a crash. Rapid acceleration or deceleration of a vehicle typically triggers an explosive device to pull a cable and rapidly rotate the retractor spool in a webbing winding direction. A webbing intake of 200 mm in approximately 10 ms is required for the pretensioner to be effective.
At these rates of acceleration the applicant has observed that the web sensor is prelocked by the operation of the pretensioner.
The web sensor has an earlier phasing geometry than the vehicle sensor so that it tends to cause engagement of the main locking member earlier than the vehicle sensor does.
It is an object of the present invention to take advantage of the earlier phasing geometry of the webbing sensor and to provide a locking mechanism which is actuated via the webbing sensor and which locks the retractor spool permanently against further webbing withdrawal. Such a locking mechanism has the advantage of preventing webbing payout in a multiple crash situation and of being a tangible sign that a pretensioner has fired and preventing re-use of the retractor after an accident.
According to the present invention there is provided a locking mechanism for a webbing retractor for a vehicle safety restraint system, the retractor comprising safety restraint webbing wound on a rotatable spool, and on inertia member mounted for rotation with the spool under normal usage conditions and means coupling the inertia member to the spool so that it rotates with the spool under normal usage conditions, and is decouplable by acceleration or deceleration forces above a predetermined level (e.g. indicative of a pretensioning operation) to decouple the inertia members and the spool and wherein holding means are operable by the inertia member to hold a locking pawl in locking engagement with the spool to lock the spool against rotation.
Preferably the retractor comprises a web sensor having a web sensor inertia element mounted to rotate with the spool and the inertia member under normal usage conditions and resiliently connected to the locking paw in such a way that when the spool is rotated faster that a predetermined speed the inertia element lags the spool and via the resilient means moves the locking pawl into locking engagement with the spool to lock the spool against rotation.
Preferably the coupling means comprise shear pins or deformable elements which nay be formed integrally with the inertia member and which shear or bend respectively under high acceleration or deceleration forces to allow rotation of the inertia member independently of the spool. Advantageously the shear pins are located in indentations or blind holes to prevent the loose parts fouling the retractor mechanism after they have fractured.
According to a particular preferred embodiment the holding means comprises an integrally moulded detent on the second inertia member. The inertia member may be provided with a spring bias adapted to bias the holding means to lock onto the locking means on operation of the mechanism of the invention. This bias could be a coiled torsion spring linking the inertia member to the web sensor inertia element. A spring catch may also be provided to positively lock the locking means: for example an integrally moulded clip on the inertia member. Parts of the mechanism may be made of zinc casting or of moulded plastic materials.
The coupling between the inertia member and the web sensor inertia element (which may each be of a general disc form) is such that during normal operation of the retractor, the inertia mean member plays no part in the function of the web sensor (and its inertia element) because the angular accelerations experienced by the mechanism during normal operation are too low to cause decoupling eg. to shear the connecting pins or deform the deformable coupling.
For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings in which: